"Our rankings have changed" that what Alexa is saying on their website. Well, it seems like good news for search engine optimizers, webmasters, web directory owners who always like to check Alexa Ranking for their websites.
Yes! Alexa have launched a new Alexa rankings system with improved methodology and algorithm to check website popularity. Website Rankings on Alexa are now based on more web sources giving better indication on popularity. Get more information at http://www.alexa.com/site/company/announcement